In recent gears, electric vehicles and hybrid vehicles have been drawing attention for the realization of a low-carbon society. As a compressor for performing the cooling of the vehicle interior in such electric vehicles and hybrid vehicles, a compressor to compress the refrigerant with the driving force of electric motor (hereinafter, referred to as an “electric compressor”) is mounted instead of a compressor to compress the refrigerant with the driving force of the engine up to that point of time.
If a high-load operating state continues in this electric compressor, a motor or a power element for supplying electric power to drive a motor is overheated. This may cause deterioration of characteristics, and the motor or the power element may be damaged. For this reason, it is necessary to detect the temperature of the motor, the temperature of the power element, the discharge temperature of refrigerant, and the like and to stop the electric compressor or restrict the operation when these temperatures exceed a threshold value.
There is a conventional electric compressor in which a thermistor to directly measure the temperature of a power element is disposed in the power element and the discharge temperature of the refrigerant is estimated on the basis of the measured power element temperature, the rotational speed of the motor, and motor phase current and voltage (for example, PTL 1). By stopping the power element when the estimated discharge temperature of the refrigerant becomes equal to or higher than a predetermined temperature (hereinafter, referred to as a “power element overheat protection operation”), it is possible to perform overheat protection of the power element.